When photographic film is stored on a small core for extended periods of time and/or at elevated temperatures, the film takes on a core set. Core set of the film causes the film to curl in a longitudinal direction when the film is removed from the core and is unconstrained.
With conventional films that include a cellulose triacetate (CT) base, most of the core set imparted to the film is removed during processing of the film. The core set is removed because the film emulsion and base both absorb significant amounts of water when exposed to water-based solutions during processing. As a result, the processed film typically exits a film processor in long strips which are not curled. These strips fall into a receptacle and then are manually carried to a photographic printer where prints of the images on the film are made.
Other types of films, such as those which include a polyethylene terepthalate (PET) or polyethylene napthalate (PEN) base, lose very little core set during processing. This is due to the fact that these types of film bases absorb very little water during processing in water based solutions. Consequently, as this type of film exits the film processor, the film tends to curl back up on itself.